A P0304 misfire typically costs about $150 to $700 to fix, depending on the root cause and labor. Simple fixes such as spark plugs or ignition coils are on the lower end, while more extensive injector work or engine repairs can push the price higher. This article explains what the code means, common fixes, and price ranges you’re likely to encounter.
What P0304 Means
The P0304 code is a generic powertrain fault indicating a misfire in cylinder 4. When the engine control unit detects irregular combustion in that cylinder, it sets the code and may trigger rough idle, reduced power, or poor acceleration. A precise fix depends on diagnosing whether the problem is related to spark, fuel, air, or a mechanical issue.
Common Causes That Trigger P0304
Misfires can stem from several root causes. The following list covers the most frequent culprits and helps estimate what repair might be needed:
- Worn or fouled spark plug in cylinder 4
- Faulty ignition coil or spark plug wire
- Clogged or leaking fuel injector for cylinder 4
- Vacuum leaks or intake gasket issues near cylinder 4
- Low compression in cylinder 4 due to piston, ring, valve, or head gasket problems
- Sensor or PCM issues affecting ignition timing or fuel delivery
Conclusion: In many cases, the fix aligns with one of these common causes, ranging from a simple plug change to more involved injector or mechanical repairs.
Cost Range: What You Might Pay
Before listing typical prices, note that diagnostic fees and regional labor rates vary. The ranges below reflect common scenarios encountered by repair shops across the country.
- Diagnostic and inspection: $50–$150
- Spark plug replacement (cylinder 4): $70–$160 total
- Ignition coil replacement (cylinder 4): $80–$250 total
- Fuel injector cleaning or replacement (cylinder 4): $200–$600
- Vacuum leak repair or intake gasket replacement: $150–$450
- Engine mechanical repair (low cylinder compression or major components): $1,000–$4,000+
Conclusion: For most passenger vehicles, many P0304 fixes fall in the hundreds of dollars, while complex mechanical problems can push the bill into the thousands. Always obtain a written estimate with parts and labor before authorizing work.
Can I DIY this?
Some fixes, like replacing spark plugs or a faulty ignition coil, are doable for a confident DIYer. However, diagnosing a misfire properly often requires professional diagnostic tools and expertise to avoid misdiagnosis and unnecessary repairs. If you’re unsure, start with simple spark plug/coil checks and then consult a shop for a precise diagnostic and quote.
Summary
The P0304 code signals a misfire in cylinder 4 and can be caused by spark, fuel, air, or mechanical issues. Repair costs vary widely—from roughly $70–$160 for basic spark plug work up to $1,000–$4,000 or more for engine-related problems. A professional diagnostic is essential to identify the exact cause and provide an accurate estimate before any major repairs.